This application claims the priority of German Patent Application, Serial No. 201 01 602.8, filed Jan. 31, 2001.
The present invention relates, in general, to a twist-beam axle, and more particularly to a twist-beam rear axle of a type having two longitudinal control arms interconnected by a double-walled transverse strut of V or U shape.
Twist-beam axles combine the advantages of a simple structure with slight spatial demands and good kinematic properties. The transverse strut for interconnecting the longitudinal control arms acts as torsion bar so as to realize a characteristic of a longitudinal control arm upon simultaneous compression and a characteristic of a semi-trailing arm upon reciprocal compression.
Various proposals have been made to so configure the transverse strut of a twist-beam axle as to be rigid on one side and to provide sufficiently low degree of torsional stiffness on the other side. German Pat. No. DE 44 16 725 A1 discloses a twist-beam axle with two rigid longitudinal control arms, which are elastically linked to the superstructure and carry two wheels. The longitudinal control arms are welded to one another by a transverse strut, which is rigid, but of low torsional stiffness. The transverse strut is made over its entire length of a tubular profile which at both ends has a cross section of high torsional stiffness and in mid-section a U, V, L, X or similar cross section of low torsional stiffness with at least a double-walled profile leg.
Another conventional twist-beam axle includes a transverse strut of V-shaped cross section. The transverse strut is welded by U-shaped transition pieces with the longitudinal control arm.
To date, twist-beam axles of conventional configuration use in a wide variety of application tubular transverse struts which have at least over a major portion of their length a V-shaped or U-shaped double-walled cross section. As a result, the need for stabilizers is eliminated. Moreover, the relative disposition of the profile relative to the longitudinal control arms allows adjustment of the running behavior in dependence on the respective chassis and thus positive modification to suit the respective type of motor vehicle. At the same time, the tubular configuration has weight advantages compared to conventional torsional profiles made of flat material.
Although continuous advances of conventional twist-beam axles have resulted in increased performance and decreased weight, there is still a need for better performance and increased service life, while yet realizing an economic configuration of the twist-beam axle.
It would therefore be desirable and advantageous to provide an improved twist-beam axle for motor vehicles, which obviates prior art shortcomings and which improves the running behavior while having a greater service life.
According to one aspect of the present invention, a twist-beam axle for motor vehicles, includes two longitudinal control arms, and a transverse strut interconnecting the longitudinal control arms and defined by a length, wherein the transverse strut has over a major portion of the length a doubled-walled cross section of one of V-shaped configuration and U-shaped configuration, thereby defining an inner profile and an outer profile, wherein the inner and outer profiles support one another at least over predetermined portions to define a contact zone therebetween for receiving a friction-reducing additive.
As the outer and inner profiles support one another, the dynamic stress behavior of the twist-beam axle is improved, thereby enhancing the running behavior of the vehicle. Torsional forces and bending forces, encountered during operation, are transmitted from the longitudinal control arms into the transverse strut for compensation. The mutual support of both profiles acts hereby in a positive way. When both wheels are compressed, a relative movement between the walls of the outer profiles and inner profiles is effected. This relative movement results in a friction between both profiles, which is lowered by the friction-reducing additive in the contact zone of both profiles. As a consequence, the twist-beam axle according to the present invention exhibits a superior static and dynamic load behavior and has a very long service life.
In addition to the friction-reducing effect, the additive provides also a corrosion protection. Suitably, the additive should have a composition that maintains effectiveness over a temperature range from xe2x88x9260xc2x0 C. to +80xc2x0 C. An example of a proper material for an additive includes an additive on ceramic bases. Useful, for example, may be an additive in the form of a metal oxide lubricant, which, after application, forms a ceramic protective film by which a reliable lubrication is ensured. Other useful examples for additives include temperature-resistant additives, which are stable at temperatures of up to more than 1,000xc2x0 C. In this way, the twist-beam axle according to the invention is capable to withstand all temperatures influences, even those encountered during manufacturing processes, such as, e.g., welding works, paint works and the like.
Basically, it is conceivable to coat only the inside surfaces of the transverse strut in the contact zones with additive. Of course, it is also possible to coat the entire inside surface. Suitably, the additive is liquid during application. However, the additive is so constituted that, already after a short time, it becomes pasty in order to avoid an uncontrolled leaking. In this way, the additive can be rationally applied during a normal manufacturing process. After application of the additive, the tube, as initial material, is shaped without removal of material into the transverse strut. As an alternative, the transverse strut may also be made in shell construction, for example, from two pressed shells, which form the outer and inner profiles and are welded together. Of course, the profile of the transverse strut may be shaped initially, and subsequently, the friction-reducing additive may be applied. As the additive is liquid, application of the additive results in a penetration into the voids and in a wetting of the surface as a consequence of the capillary effect.
According to another feature of the present invention, the additive may be a mixture, in particular an emulsion-like or oil-containing mixture, and may contain hard mineral constituents, for example, ceramic pigments or corundum, silicon carbide, or aluminum oxide. Currently preferred is a mixture of oils or grease, ceramic pigments, antiseize agents and volatile ingredients. The volatile ingredients evaporate after application so that the initially flowing mixture is transformed into a pasty mass. When subjected to external pressure, the hard constituents are able to penetrate the surface of the transverse strut in the contact zone. In the contact zone, the hard constituents form an area of very low friction value in conjunction with the antiseize agents. The thus-modified surfaces do not experience seizing.
A twist-beam axle according to the present invention may be made of steel as well as of light metal or light metal alloy. As a consequence of the V-shaped or U-shaped cross section of the twist-beam axle according to the invention, the torsional properties of the transverse strut are improved while yet reducing the weight. The running behavior, in particular the camber change and bump toe-in during alternating compression and/or turn-in ability of the twist-beam axle are improved, when negotiating curves. Suitably, the transverse strut is made of a tubular profile, which at both ends has a cross section of high torsional stiffness and in mid-section a U-shaped or V-shaped double-walled cross section of low torsional stiffness. This configuration of the transverse strut results in a better distribution of the forces. Encountered bending and torsion forces are sufficiently absorbed by the longitudinal control arms.